Sheet handling devices are widely used in image reproduction systems such as analog and digital copiers and radiographic laser printers. In such devices, sequential sheets are output to one or more output bins. In the case of multiple output bins, such as sorters, the sheets are selectively deflected from a main sheet transport path into secondary sheet transport paths which branch off the main sheet transport path. In order to detect sheet jamming in one of the sheet transport paths, sheet sensors are located along the sheet transport paths to detect the presence or absence of a sheet. Typically, individual sensors are located along the main path and along each secondary path. The use of several sensors adds expense and complexity to the sorter control system. Japanese Patent Application no. 60-035163, publication date Aug. 28, 1986, inv. Michio, Japanese Patent Application no. 2000-072323, publication date Mar. 7, 2000, inv. Tomoyuki et al., Japanese Application no. 08-247677 and U.S. Pat. No. 6,325,371B, filed Aug. 31, 1999, inv. Araki et al., disclose sorters having sheet sensors which do not solve this problem.
Japanese Patent Application no. 54-124364, publication date, Apr. 28, 1981, inv. Yotaro et al. discloses a sorter having a single light source, light detector positioned to determine whether any of the sorter bins contain sheets. Once a sheet has entered any bin, the sensor is disabled and cannot detect sheet jams.
There is thus a need for a simple and inexpensive sheet detection system for a sorter that can detect sheet jams in the main sheet path and secondary sheet paths to the output bins.